A terrified Long Island mom’s quick-thinking but devastatingly painful choice helped save the life of her toddler son over the summer — and eventually revealed the exceptionally rare condition he suffers from. “Picture breathing through a milkshake straw, then breathing through a regular straw, then trying to breathe through a coffee straw,” Maria Carlin, 36, recently told The Post of her 4-year-old Jack’s harrowing experience in late July. “We got to a point where I said to myself, ‘It doesn’t